Process for polymerizing acrylonitrile in the presence of sulfonic acids



United States atent,

PROCESS FOR POLYMERIZING ACRYLGNITRILE IN THE PRESENCE F SULFONIC ACIDSHarry W. Coover, Jr., Joseph B. Dickey, and Theodore E. Stanin,Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N. Y.,a corporation of New Jersey No Drawing. Application August 25, 1952, t lSerialNo. 306,311

13 Claims. (Cl. 260'88.7)

Polymers of acrylonitrile and numerous methods for their preparationhave beendescribed previously in the chemical literature, and bothforeign and domestic patents. More recently, it has been proposed to usepoly mers of acrylonitrile in the manufacture of synthetic fibers orfilms. The use of these polymers for this purpose has been somewhatlimited due to the difiiculty of obtaining a polymer having the desiredsolubility properties, as well as the property of giving uniformlycolorless fibers when their solutions are spun through a spinneret intoa precipitating bath. The polymers of acryl onit'rile previouslyemployed have an undesirable tendency to give gelled particles whendissolved in a solvent, such as dimethylformamid'e. These gelledparticles can be dissolved to some degree by heating, however, theheating causes discoloration of the fibers spun from a heated solution,and if the solution is cooled to room temperature again, the gelledparticles generally reappear; If these gelled particles are allowed toremain suspended in the solution the spinnerets become clogged duringthe spinning and the fiber obtained is uneven and of low tensilestrength. Equally important, the fibers produced by spinning solutionsof polymers of acrylonitrile made by the methods heretofore employed arenot white in color, but have an undesirable brownish color which makesthem difficult to use without further treatment, which materially lowersthe strength and uniformity of the fibers. It can thus be seen that itis highly desirable to provide a process for manufacturing polymers ofacrylonitrile which give uniform, gel-free solutions, and whosesolutions when spun into a coagulating bath give lustrous, colorlessfibers.

A further difficulty encountered in working with polymers ofacrylonitrile containing large quantities of acrylonitrile in th polymermolecule (usually on the order of from 80 to 100 per cent by weight) hasbeen the property of these polymers to show such limitedsolubilityinlthe usual organic solvents, such as acetone.

This difliculty has served to stimulate a widespread program ofexperimentation in the art to find suitable solvents that would increasethe utility of polymers of ac'rylon'itrile which havelong beenrecognized as having properties of considerable economic importance.Dimethylformamide is perhaps one of the more common solvents which is inuse at present for dissolving these polymers; however, this substance istoxic to use, thus constituting a hazard which has to be reckoned withwhen used in a confined area, such as a factory. Dime'tlfylformamide issubject to further objection because of. its laclt of stability andtendency to release dimethyh amine. A solvent which would overcome thesediflicub ties would, therefore, be most useful in increasing the ice 1use of polymers of acrylonitrile in the preparation of white fibers andcolorless films.

It is, accordingly, an object of our invention to pro vide an improvedprocess for preparing polymers of acrylonitrile. A further object is toprovide polymers of acrylonitrile which can be dissolved in solvents togive gel-free solutions. A still further object is to provide solutionsof polymers of acrylonitrile which give lustrous, colorless fibers whenspun into a coagulating bath. 'Another object is to provide a solventfor dissolving polymers of acrylonitrile, which is not as toxic asdimethylformamide and gives stable solutions. Other objects will becomeapparent from a consideration of the following description and examples.

According to the process of our invention, we accomplish the aboveobjects by polymerizing acryl'onitril'e (either homopolymerizing orinterpolymerizing) in an aqueous solution in the presence of an oxygenacid of sulfur selected from those represented by the following generalformula:

trile can be readily dissolved in N,N-diinethylacetamide to givesolutions which are not as toxic as dimethyl formamide, and whichovercome other difliculties inherent in the use of dimethylformamide.For reasons Which are not readily apparent, the polymers ofacrylonitrile previously prepared by prior art processes will notdissolve in N,N -dimethylacetamide sufiiciently to give so lutionssuitable for spinning, although they do dissolve completely indimethylformamide. Since N,N-dimethyla'cetamide was not a suitablesolvent for the polymers previously prepared, it was most surprising tofind that it was excellently suited for dissolving polymers prepared bythe present process. The preparation of polymer solutions fromN,N-dimethylac'etamide is, therefore, closely related to our improvedprocess for preparing polymers of acrylonitrile.

In our polymerization of acrylonitrile, we advantageously add theacrylonitrile to a quantity of water which is sufiicient to dissolve asubstantial portion of theacrylonitrile. Generally the amount of waterpresent dissolves about per cent of the acrylonitrile added, theremaining acrylonitr ile forming a dispersion in the aqueous solution.As the polymerization proceeds, the polymerized acrylonitrileprecipitates out of solution and more of the dispersed acrylonitrilegoes into solution. In practicing our invention, it is not essentialthat all of the acrylonitrile be dissolved in the aqueous reactionmedium atone time, since a dispersion of acrylonitrile inherently hassome of the acrylonitrile dissolved in the aqueous phase. The oxygenacid of sulfur selected from those described above can be dissolved inWater and the acrylonitrile then added, or the acrylo'nitrile can beadded to the water first and the oxygen acid of sulfur addedsubsequently. The quantity of oxygen acid of sulfur selected from thosedescribed above varies and depends on the volume of Water present, thequantity of materials being polymerized, etc. Suflicient oxygen acid ofsulfur selected from those described above should be used to maintainapHof from 1 to 3 throughout the polymeriza tion, since we have foundpolymerizations carried out outside this range do not give polymershaving desirable characteristics, even where oxygen acid of sulfur isemployed. We have found the polymers having especially desirableproperties are obtained when the polymerization is carried out at a pHof from 1.5 to 2.0, although the broader range of l to 3.0 is adequatefor most purposes.

The polymerization iseffected in the presence of an alkali metalpersulfate polymerization catalyst (i. e. persulfates of the elements ofGroup I of the periodic table, such as sodium, potassium, lithium, etc),or ammonium persulfatc, and a water-soluble inorganic compound of sulfurselected from the group consisting alkali metal and ammonium bisulfites,such as sodium bisulfite, potassium bisulfite, ammonium bisulfite, etc.;alkali metal and ammonium sulfites, such as sodium suhite, potassiumsulfite, ammonium sulfite, etc; alkali metal and ammonium thiosulfates,such as sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate,etc; alkali metal sulfides, such as sodium sulfide, potassium sulfide,sodium hydrosulfidc (NaSl-I), potassium hydrosulfide (KSH), etc;ammonium sulfides, such as ammonium sulfide and ammonium hydrosulfide,hydrogen sulfide (H28), and sulfur dioxide. The term alkali metal asused herein is intended to define the metals of Group I of the periodictable of the elements. The persulfate polymerization catalyst isactivated by the Water-soluble inorganic compound of sulfur having areducing action, which lowers the induction period preceding theinitiation of the polymerization. The activators are also useful inproviding a convenient method for regulating the molecular weight of thepolymer, the molecular weight being a function of the quantity ofactivator employed. The quantity of persulfate catalyst can be varied,depending on the conditions of polymerization and the quantity ofmaterial being polymerized. Generally, we have found that from 0.5 to2.5 per cent by weight, based on the materials being polymerized, issufi'icient for the purposes of our invention. Especially usefulpolymers have been obtained when about 2 per cent by weight ofpersulfatc was employed. The quantity of water-soluble inorganiccompound of sulfur used as an activator can be varied, the amount usedbeing somewhat arbitrary. Generally, from 0.5 to7 molar equivalents ofthe activator for each molar equivalent of persulfate catalyst, areadequate for practicing the process of our invention. A more limitedrange which We have found to be useful is from 1. to 2 molar equivalentsof the activator for each molar equivalent of the persulfatepolymerization catalyst, especially where from 1 to 2 per cent byweight, based on the total weight of polymerizable materials present, ofpersulfate polymerization catalyst is used. Larger or smaller amounts ofthe activator can be used, although there is ordinarily no advantage indoing so. About 5 molar equivalents of activator for each equivalent ofpersulfate has been found to give especially good results. The amount ofoxygen acid of sulfur selected from those described above is usuallyfrom 1 to 3 molar equivalents for each molar equivalent of thepersuifate catalyst and the activator combined.

The polymer which precipitates from the aqueous solution is separatedand Washed several times to free the polymer from excess acid andoccluded catalyst or activator. It is not necessary to remove all of theoxygen acid of sulfur from the polymer, since we have found that smallamounts actually have a'beneficial effect when the polymer is dissolvedin a solvent for spinning. This process is more fully described in ourapplication Serial No. 49,655, filed on September 16, 1948, now U. S.Patent 2,503,245, dated April ll, 1950.

The following examples will more fully describe the manner whereby wecarry out the process of our invention.

EXAMPLE I 2 guns. (0.013 mole) of benzenesulfonic acid were dissolved in200 cc. of distilled water, and 0.2 gm. (0.001 mole) of ammoniumpersulfate and 0.4 gm. (0.004 mole) of sodium bisulfite were added anddissolved. While slowly stirring the solution 20 gms. (0.38 mole) offreshly distilled acrylonitrile were added. The polymerization beganalmost immediately as evidenced by the formation of a fine, whiteprecipitate. After all of the acrylonitrile had gone into solution, thestirring was discontinued. At the end of 16 hours, the reaction mixturewas filtered with the aid of suction, and the filter cake washed free ofacid with distilled water and dried. The polyacrylonitrile dissolvedreadily in dimethylformamide and N,N-dimethylacetamide to form smooth,clear viscous solutions, which gave lustrous, white fibers when spuninto a precipitating bath.

EXAMPLE II 2 gms. (0.012 mole) of p-toluenesulfonic acid were dissolvedin 200 cc. of distilled water, and 0.2 gm. (0.001 mole) of ammoniumpersulfate and 0.4 gm. (0.004 mole) of sodium bisulfite were added anddissolved. While slowly stirring the solution 20 gms. (0.38 mole) offreshly distilled acrylonitrile were added. The polymerization beganalmost immediately as evidenced by the formation of a fine, whiteprecipitate. After all of the acrylonitrile had gone into solution, thestirring was discontinued. At the end of 16 hours, the reaction mixturewas filtered with the aid of suction, and the filter cake washed free ofacid with distilled water and dried. The polyacrylonitrile dissolvedreadily in dimethylformamide and N,N-dimethylacetamide to form smooth,clear viscous solutions, which gave lustrous, White fibers when spuninto a precipitating bath.

EXAMPLE HI 2 gms. (0.021 mole) of methanesulfonic acid were dissolved in200 cc. of distilled Water and 0.2 gm. (0.001

mole) of ammonium persulfate and 0.4 gm. (0.004 mole) of sodiumbisulfite were added and dissolved. While slowly stirring the solution20 gms. (0.38 mole) of freshly distilled acrylonitrile were added. Thepolymerization began almost immediately as evidenced by the formation ofa fine, white precipitate. After all of the acrylonitrile had gone intosolution, the stirring was discontinued. At the end of l6 hours, thereaction mixture was filtered with the aid of suction, and the filtercake washed free of acid with distilled water and dried. Thepolyacrylonitrile dissolved readily in dimethylformamide andN,N-dimethylacetamide to form smooth, clear viscous solutions, whichgave lustrous, white fibers when spun into a precipitating bath.

EXAMPLE IV 2 guns. (0.018 mole) of cthanesulfonic acid were dissolved in200 cc. of distilled water, and 0.2 gm. (0.001 mole) of ammoniumpersulfate and 0.4 gm. (0.004 mole) of sodium bisulfite were added anddissolved. While slowly stirring the solution 20 gms. (0.38 mole) offreshly distilled acrylonitrile were added. The polymerization beganalmost immediately as evidenced by the formation of a fine, whiteprecipitate. After all of the acrylonitrile had gone into solution, thestirring was discontinued. At the end of 16 hours, the reaction mixturewas filtered with the aid of suction, and the filter cake washed free ofacid with distilled water and dried. The polyacrylonitrile dissolvedreadily in dimethylformamide and N,N-dimethylacetamide to form smooth,clear viscous solutions, which gave lustrous, white fibers when spuninto a precipitating bath.

The following examples illustrate some of the more conventional methodsfor making polyacrylonitrilc which have heretofore been used in theprior art.

EXAMPLE V 200 gms. of freshly distilled acrylonitrile were added to 600cc. of distilled water and the mixture stirred slowly to effectsolution. While stirring 0.2 gm. of potassium persulfate and 2 grns. ofdodecyl mercaptan were added and the mixture heated to C. A precipitatebegan to. form almost at once, and'whcn. no more precipitate separated,heating was discontinued, and thereaction mixture was cooled andfiltered. The filter cake was Washed with water and then dried. The drypolyacrylonitril'e was soluble indimethylformamide on heating, but thesolution of the polyacryl'onitrile in the dimethylforma-mide containedgel-like particles in suspension, and when spun into a coagulating bathgave a yarn of light brown color.

1 EXAMPLE VI A 5 gi'ns. of freshly distilled acrylonitrile were addedto. 45 cc. of distilled water, and. the mixture stirred to eflfectsolution. The mixture was then stirred while 1 gm. of hydrogen peroxidewas added. The air above the mixture was replaced with nitrogen gas, andwhen the mixture was warmed. a precipitate began to form. When.

no more. precipitate separated out, heating was discon: tinued and thereaction mixture was cooled and filtered. The filter cake was washed.with distilled water and then dried; The dry polyacrylonitrile wassoluble in dimethylformamide on heating, but the solution ofpolyacrylonitrile in dimethylformamide when. spun into a coagulatingbath gave. a: yarn having a; light tan color.

EXAMPLE VII giveav light colored solution. upon-heating, but upon. coolingt-he solution, gel-likeparticles formed. Thepolymer did not. givesolutions suitable for spinning when added. to- N,N-dimethylacetamide.When theisolutiontof polyacrylonitrile in dimethylformamide was spuninto a coagulating bath, light tan-colored fibers were obtained.

To further demonstrate the marked improvement in properties in thepolymer obtainable in ourv process. over those: obtained previously, thetransmission of light by the solutions of, polyacrylonitrile obtained inthe above examples was measured. The amount of transmission proved to bea reliable means for measuring the extent of solutiorn and detectionofany irregularities present. The" Blue light; transmission is aparticularly useful method of illustratingthe solution properties, sinceblue light is more highly absorbed in a discolored solution than' theother colors of'the spectrum. The results obtained are given in thetable below:

Unh cated Solutions, 1 Percent Blue light transmltted Polymer. ofExample methylacetamide without heating to form smooth, gel-fre'esolutions, which give lustrous white fibers when spun into 7 ml. of a1.0%

eriods of heating being" particularly undesirable; Polymers preparedaccording to our process or" the other dis-- sol-v'e readily in eitherdiniethyl formamide or N,N-di= a coagulating bath. Another advantage inthe polymers prepared according to our process is that they need not beground to such small particle size to effect solution as the polymersprepared by methods heretofore commonly employed (which generally haveto be ground to from 150 to 200. mesh particle size). As noted above, incontrast to the white fibers which can be ob'tainedfr'om the polymersprepared according to the process of our invention, those obtained fromthe polymers prepared by the methods previously employed. are lighttanin. color.

It has been. previously proposed to polymerize ac'rylonitrile accordingto a process similar to that described in: Examplesl to IV above, exceptthat sulfuric acid is used to modify the pH in lieu of the acids setforth in those examples. While sulfuric acid does provide manyadvantages not heretofore obtainable, the induction;

period (i. e. timebefore polymerization begins, all ingredients ofpolymerization mixture being present) is high when sulfuric acid isused, and the rate of polymerization is slow. The following. examplescompare the induction periods and rates of polymerization of variousmethods using sulfuric acid. or one of the oxygen acids of sulfurselected from, thosedescribed above.

Efiect 0 various acids on the speed of polymerization l of acrylonitrileThe following solutions were prepared: 7

EXAMPLE VIII 20 ml. of distilled water, 2.0 ml. of Solution A, 10ml. ofa 1.0% aqueous solution of potassium persulfat'e, ml. of acrylonitrilemonomer and 1.0 ml. of a 1.0% aqueous solution of potassium bisulfitewere placed in a glass vial which had been washed with distilled water.The vial 'was equipped wi'th a polyethylene-lined cap; After thesolution was completed by shaking, the time elapsed beforepolymerization began was measured, the polymerization being evidenced bythe formation of a milky precipitate. The induction period for thepolymerization was 27 minutes, i. e. 27 minutes elapsed before" theonset of polymerization.

EXAMPLE IX 20 ml. of distilled water, 2.0 m1. ofSolutionB, 1.0 ml. of a1.0% aqueous solution of potassium persulfate; 1.0-ml. of acrylonitrilemonomer and 1.0 of a 1.0% aqueous solution of potassium bisulfite wereplaced in a glass vial whichhad been washed with distilled water. Thevial was e'quiipped with a polyethylene-lined cap; After the solutionwas completed by shaking, the time elapsed before polymerization: beganwas'measured, the polymerization being evidenced by the formation of amilky precipitate. merization-exceeded4 hours; i. e. 4 hours elapsedbefore the onset of polymerization.

EXAMPLE X I 20. mlof distilled water, 2.0 ml. of Solution-C, L0 aqueoussolution of potassium persulfat'e; 1.0 of acrylonitrile monomer. and1.0-ml..of-a 1 .0% aqueous solution. of potassium bisulfite wereplacedin a glass vial which had been washed with distilled wa- Theinduction period for the polyter. The vial was equipped with apolyethylene-lined cap. Afterthe solution was completed by shaking, thetime elapsed before polymerization began was measured, thepolymerization being evidenced by the formation of a milky precipitate.Theinduction period for the polymerization was 41 minutes, i. e. 41minutes elapsed before the onset of polymerization.

Rate of polymerization The rate of polymerization of acrylonitrilemonomer was determined by polymerization in a vacuum-jacketed flask,using the following formation:

40.0 ml. of distilled water 4.0 ml. of Solution A, B or C 2.0'ml. ofacrylonitrile monomer 2.0 ml. of a 1.0% aqueous solution of potassiumpyrosulfite (metabisulfite) 2.0 ml. of a 1.0% aqueous solution ofpotassium persulfate In each of the three formulations (i. c. with acidof Solution A, B or C), the water and acid were boiled under vacuum toremove all oxygen and the flask was filled with nitrogen gas. Themonomer, catalyst (persulfate) and activator (pyrosulfite) were injectedthrough a butyl rubber, self-sealing gasket. The temperature rise ineach of the three formulations was measured over a given period (60minutes). The temperature rise was determined inasmuch as the rate ofpolymerization was found to be roughly proportional to the temperaturerise'over a given period. Previous calibration of the, apparatus showedthat a temperature rise of 1.0 C. corresponded to a conversion of12.3%.. The re, sults of the polymerizations with the acids of SolutionsA, B and C are. tabulated below.

While our process has been described above with particular reference tothe homopolymerization af acrylonitrile, it is to be understood that itis likewise useful in the interpolymerization of acrylonitrile withother polymerizable substances, such as acrylic acid, acrylamide, ethylacrylate, vinyl acetate, vinyl chloride, styrene, etc., to giveinterpolymers which cannot be dissolved by the usual organic solvents.Such interpoly mers should usually contain at least 80 per cent byweight of acrylonitrile in the polymer molecule, since polymerscontaining less than this amount melt at too low temperatures to warranttheir use in the preparation of fibers or yarns. Generally from 6 to 9per cent by weight of the other polymerizable material in theinterpolymer is adequate for the purposes of our invention.lnterpolymers, containing less than 80 per cent by weight ofacrylonitrile in the polymer molecule (e. g. from 70 to 73 per cent),also can advantageously be prepared according to the process of ourinvention, and these interpolymers are useful where an unusually highmelting polymer is not required, as, for example, in the preparation offilms or sheets. The polymers prepared in accordance with the process ofour invention are outstanding in their solubility properties, especiallyin N,N-dimethylacetamide, a solvent in which the polyacrylonitrilepreviously prepared is not soluble to a sufficient degreeto permitspinning of fibers therefrom. As shown above, N,N-dimethyl acetamide isparticularly useful in dissolving the polymers obtained in our process,since it is materially less toxie than dimethylformamide and givessolutions havingwherein R represents a member selected from the groupconsisting of an alkyl group of from 1 to 2 carbon atoms and amononuclear aromatic hydrocarbon group of the benzene series containingfrom 6 to 8 carbon atoms, to maintain a pH of from 1 to 3 during thepolymerization and a water-soluble inorganic compound of sulfur selectedfrom the group consisting of alkali metal bisulfites, ammoniumbisulfite, alkali metal sulfites, ammonium sulfite, alkali metalthiosulfates, ammonium thiosulfate, alkali metal sufides, ammoniumsulfides, hydrogen sulfide and sulfur dioxide.

2. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in a solution in the presence of a persulfatepolymerization catalyst, a sufficient quantity of an acid of sulfurselected from those represented by the following general formula:

wherein R represents an alkyl group of from one to two carbon atoms, tomaintain a pH of from 1 to 3 during the polymerization and aWater-soluble inorganic'cornpound of sulfur selectedfrom the groupconsisting of alkali metal bisulfites, ammonium bisulfite, alkali metalsulfites, ammonium sulfite, alkali metal thiosulfates, ammoniumthiosulfate, alkali metal sulfides, ammonium sulfides, hydrogen sulfideand sulfur dioxide.

3. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in a solution in the presence of a persulfatepolymerization catalyst, a sufficient quantity of an acid of sulfurselected from those represented by the following general formula:

wherein R represents a mononuclear aromatic hydrocar bon group of thebenzene series containing from 6 to 8 carbon atoms, to maintain a pH offrom 1 to 3 during the polymerization and a water-soluble inorganiccompound of sulfur selected from the group consisting of alkali metalbisulfites, ammonium bisulfite, alkali metal sulfites, ammonium sulfite,alkali metal thiosulfates, ammonium thiosulfate, alkali metal sulfides,ammonium sulfides, hydrogen sulfide and sulfur dioxide.

4. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufficient quantity of an acidofsulfur selected from those represented by the following. generalformula:

from those represented by the following general formula:

wherein R represents a mononuclear aromatic hydrocarbon group of thebenzene series containing from 6 to 8 carbon atoms, to maintain a pH offrom 1 to 3 during the polymerization and an alkali metal bisulfite.

6. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufiicient quantity ofethanesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

7. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufiicient quantity ofmethanesulfonic acid to main tain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

8. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a suflicient quantity ofbenzenesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

9. A process for preparing polymers of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufiicient quantity ofp-toluenesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

10. A process for preparing a homopolymer of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufiicient quantity ofethanesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

11. A process for preparing a homopolymer of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a suflicient quantity ofmethanesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

12. A process for preparing a homopolymer of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a suflicient quantity ofbenzenesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

13. A process for preparing a homopolymer of acrylonitrile comprisingpolymerizing acrylonitrile in an aqueous solution in the presence of apersulfate polymerization catalyst, a sufficient quantity ofp-toluenesulfonic acid to maintain a pH of from 1 to 3 during thepolymerization and an alkali metal bisulfite.

References Cited in the file of this patent UNITED STATES PATENTS2,462,422 Plambeck Feb. 22, 1949 2,628,223 Richards Feb. 10, 1953

1. A PROCESS FOR PREPARING POLYMERS OF ACRYLONITRILE COMPRISINGPOLYMERIZING ACRYLONITRILE IN A SOLUTION IN THE PRESENCE OF A PERSULFATEPOLYMERIZATION CATALYST, A SUFFICIENT QUANITY OF AN ACID OF SULFURSELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: